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GH4698 — old drawing name GH698, Russian ЭИ698 / ХН73МБТЮ — is a Ni-Cr base, γ′ precipitation-hardened wrought superalloy under GB/T 14992-2005 (ISC H46980). It is not Waspaloy, not Inconel 718, not GH3044. It was bred from the GH4033 family by cutting Cr from ~20% to 13–16%, raising Al+Ti, and adding Nb 1.8–2.2% plus Mo 2.8–3.2%, to push the useful disk-service band from 650℃ up to 750–800℃ while keeping a forgeable wrought microstructure. In plain terms: it is the Chinese aero-engine turbine-disc alloy for the 750℃ wheel rim, the one you specify when 718 is dead and Waspaloy is overkill on cost.
1. Chemistry Envelope (GB/T 14992-2005, wt%)
|
Element |
Min |
Max |
Role |
|---|---|---|---|
|
Ni |
— |
Balance (~52–62) |
FCC γ matrix, γ′ host |
|
Cr |
13.0 |
16.0 |
Cr₂O₃ scale, 800℃ oxidation floor |
|
Co |
— |
(not in GB spec; some mill variants 9–11, base grade 0) |
— |
|
Mo |
2.80 |
3.20 |
Solid-solution drag, γ′ stability |
|
Al |
1.30 |
1.70 |
γ′ [Ni₃(Al,Ti,Nb)] former |
|
Ti |
2.35 |
2.75 |
γ′ former, dominant |
|
Nb |
1.80 |
2.20 |
Substitutes into γ′, refines particles, NbC pinning |
|
C |
— |
0.08 |
M₂₃C₆ / MC at boundaries |
|
Fe |
— |
2.00 |
Impurity control |
|
B |
— |
0.005 |
Grain-boundary cohesion |
|
Mg |
— |
0.008 |
Deoxidizer, cleans boundaries |
|
Ce |
— |
0.020 |
Oxide-scale adherence |
|
Zr |
— |
0.05 |
Boundary purification |
|
Mn / Si |
— |
0.40 / 0.60 |
Process residuals |
|
P / S |
— |
0.015 / 0.007 |
Harmful trace |
|
Cu |
— |
0.07 |
Residual |
Al+Ti ≈ 3.65–4.45%, γ′ volume fraction 20–30%. No Co in the base Chinese grade — that is the first thing Western readers trip on when they try to map it to Waspaloy (which has Co 12–15%). GH4698 wins creep at 750℃ with Nb+Mo instead of Co.
2. What "Complete" Heat Treatment Means
GH4698 has no single heat-treat line; the route is tied to the part class.
Aero disk forging (HB/Z 140, GJB 5280): 1120℃±10℃ × 8 h AC → 1000℃±10℃ × 4 h AC → 775℃±10℃ × 16 h AC. This is the canonical "standard triple" everyone quotes.
General aero forging: 1110–1130℃×8–8.5h AC + 990–1010℃×4–4.5h AC + 765–785℃×16–16.5h AC.
Fastener bar: 1100–1120℃×8h AC + 1000℃×4h AC + 775℃×16h AC.
Gas-turbine large disc (Q/GYB 665/666/667): triple above + 700℃×16h AC (second low-temp age for stress-relaxation).
Forbidden: soak >1150℃ (grain runaway), slow cool through 450–850℃ (continuous grain-boundary carbide film, embrittlement).
Annealed-only or "solution only" GH4698 is not a finished engineering material — Rp0.2 drops ~300 MPa. PO must name the exact route.
3. Mechanical Floor (Standard Triple, Typical Mill Values)
Density 8.25–8.32 g/cm³; melt 1330–1380℃; E 219–224 GPa (20℃), ~170 GPa (800℃)
RT: Rm 1120–1300 MPa, Rp0.2 705–1050 MPa, A₅ 15–24%, HB 285–360
550℃: Rm ~1000–1127 MPa, Rp0.2 ~647–706 MPa
650℃: Rm ~990–1107 MPa, Rp0.2 ~617–725 MPa
750℃: Rm 794–902 MPa, Rp0.2 617–696 MPa, A₅ 6–22%
800℃: Rm 666–745 MPa, Rp0.2 568–637 MPa
Stress rupture: 750℃/412 MPa >100 h (typical 100–200 h+), 750℃/530 MPa >100 h class; 800℃/314 MPa 45–90 h; 700℃/685 MPa 50 h+ class
Creep: 750℃/500 MPa, 1000 h, residual strain ≤0.1% (optimized heats)
The 750℃ number is the anchor. Research papers on 300 h/750℃/300 MPa rupture show γ′ coarsening begins — which is why the honest long-term service ceiling is 750℃ for stressed rotatives, 800℃ as the hard redline, 850℃ only as transient/peak.
4. Oxidation and Corrosion Reality
800℃ static air: oxidation rate <0.1 g/(m²·h), Cr₂O₃ (+minor Al₂O₃/TiO₂) adherent; 800℃ is comfortable for the skin.
900℃: short-time only; Cr₂O₃ starts volatilizing, γ′ solvus (~1000℃) still above but strength gone.
Sulfurous combustion gas (SOx trace): ~0.03 mm/a at 800℃, acceptable for aero hot section, behind GH5188/Hastelloy X in marine hot corrosion.
Not a chemical-corrosion alloy: no C-276, no 625. Seawater, H₂SO₄, HCl — wrong job. It is bought for 750℃ centrifugal load, not for pickling tanks.
5. Temperature Band, Honestly
≤650℃: GH4169 is cheaper and welds better; GH4698 is over-qualified.
650–750℃: GH4698's home — turbine disk rim, compressor rear stage, bearing ring.
750–800℃: long-term stressed redline; 800℃/200 MPa steady creep rate <1×10⁻⁸ s⁻¹.
800–850℃: low-stress static or short/mid-time peak (combustor support, not disk rim).
>850℃: exit; go GH4738/Waspaloy (815℃ disk) or powder metallurgy.
6. GH4698 vs GH4738 vs GH4169 (the only comparison that matters)
|
Axis |
GH4698 (GH698) |
GH4738 (Waspaloy) |
GH4169 (718) |
|---|---|---|---|
|
Base |
Ni-Cr, no Co |
Ni-Cr-Co 12–15 |
Ni-Fe-Cr |
|
γ′ former |
Al+Ti+Nb |
Al+Ti, Co-stab |
Nb (γ″)+γ′ |
|
Cr % |
13–16 |
18–21 |
17–21 |
|
Long-term ceiling |
750℃ (800 redline) |
815℃ |
650℃ |
|
750℃ Rp0.2 |
~620–690 MPa |
~590 MPa (but 815℃ still 500+) |
~860 (but γ″ dying) |
|
Weldability |
Poor (SAC risk, re-HT needed) |
Poor |
Excellent |
|
Cost position |
Mid-high |
Highest |
Mid |
GH4698 is the answer when the wheel runs at 750℃ and you cannot justify Waspaloy's Co bill, but 718 has already fallen out of the sky.
7. Product Forms and Spec Chain
Mother grade: GB/T 14992-2005 H46980
Bar: YB/T 5245 (general), GJB 3165 (aero load), GJB 2611 (cold-drawn), Q/GYB 05011
Plate/sheet: GB/T 14995/14996, GJB 3317/1952A
Disk/ring forging: GJB 5280, GJB 3782, HB 5285, Q/GYB 05025/05033
Heat-treat practice: HB/Z 140
Melt route for disk: VIM + VAR; ESR acceptable for static bar
No UNS, no AMS direct number. Export MTR reads: "GH4698 (GH698) / ЭИ698, GB/T 14992 H46980, no UNS/AMS counterpart, chemistry per GJB 3165."
